tests/make: replace 'variable expressions' with 'expressions'

make: show realistic invalid line in error message

Previously, the error message 'Invalid line' showed only the expanded
line, which might or might not show the actual problem. To be more
helpful, add the unexpanded line to the error message in case they
differ.

Remove the special handling of invalid lines that result from merge
conflicts. RCS is not commonly used anymore, and mentioning CVS was too
specific. By echoing the whole line, the patterns '<<<<<<' and '>>>>>>'
are clear enough to hint at the problem.

make: add more details to error message about invalid lines

tests/make: extend test suite, move old tests to 2020 scheme

The tests from envfirst.mk are now in opt-env.mk.
The tests from modword.mk are now in varmod-select-words.mk.

tests/make: extend tests for parsing makefiles

make(1): add tests for edge cases when parsing directives

make(1): move tests from directives.mk to separate tests

make(1): describe the purpose of each newly added unit test dummy

make(1): add dummies for fine-grained tests, one per single feature

The test names have been derived from the current manual page.

All these tests are dummies right now, and the code from the existing
tests will be moved into the new tests step by step.

This is done to prevent modmisc, escape, varmod-edge and varmisc from
growing without any bounds, and to reduce the side-effects of one test
to the others.

make: show realistic invalid line in error message

Previously, the error message 'Invalid line' showed only the expanded
line, which might or might not show the actual problem. To be more
helpful, add the unexpanded line to the error message in case they
differ.

Remove the special handling of invalid lines that result from merge
conflicts. RCS is not commonly used anymore, and mentioning CVS was too
specific. By echoing the whole line, the patterns '<<<<<<' and '>>>>>>'
are clear enough to hint at the problem.

make: add more details to error message about invalid lines

tests/make: extend test suite, move old tests to 2020 scheme

The tests from envfirst.mk are now in opt-env.mk.
The tests from modword.mk are now in varmod-select-words.mk.

tests/make: extend tests for parsing makefiles

make(1): add tests for edge cases when parsing directives

make(1): move tests from directives.mk to separate tests

make(1): describe the purpose of each newly added unit test dummy

make(1): add dummies for fine-grained tests, one per single feature

The test names have been derived from the current manual page.

All these tests are dummies right now, and the code from the existing
tests will be moved into the new tests step by step.

This is done to prevent modmisc, escape, varmod-edge and varmisc from
growing without any bounds, and to reduce the side-effects of one test
to the others.

tests/make: extend test suite, move old tests to 2020 scheme

The tests from envfirst.mk are now in opt-env.mk.
The tests from modword.mk are now in varmod-select-words.mk.

tests/make: extend tests for parsing makefiles

make(1): add tests for edge cases when parsing directives

make(1): move tests from directives.mk to separate tests

make(1): describe the purpose of each newly added unit test dummy

make(1): add dummies for fine-grained tests, one per single feature

The test names have been derived from the current manual page.

All these tests are dummies right now, and the code from the existing
tests will be moved into the new tests step by step.

This is done to prevent modmisc, escape, varmod-edge and varmisc from
growing without any bounds, and to reduce the side-effects of one test
to the others.

tests/make: extend tests for parsing makefiles

make(1): add tests for edge cases when parsing directives

make(1): move tests from directives.mk to separate tests

make(1): describe the purpose of each newly added unit test dummy

make(1): add dummies for fine-grained tests, one per single feature

The test names have been derived from the current manual page.

All these tests are dummies right now, and the code from the existing
tests will be moved into the new tests step by step.

This is done to prevent modmisc, escape, varmod-edge and varmisc from
growing without any bounds, and to reduce the side-effects of one test
to the others.

make(1): add tests for edge cases when parsing directives

make(1): move tests from directives.mk to separate tests

make(1): describe the purpose of each newly added unit test dummy

make(1): add dummies for fine-grained tests, one per single feature

The test names have been derived from the current manual page.

All these tests are dummies right now, and the code from the existing
tests will be moved into the new tests step by step.

This is done to prevent modmisc, escape, varmod-edge and varmisc from
growing without any bounds, and to reduce the side-effects of one test
to the others.